Earth boring



Jan. 20, 1959 F. W: CRAWFORD EARTH BORING 2 Sheets-Shet 1 Original FiledFeb. 25, 1946 INVENTOR. l4 EWCRAWFORD .v e? A TORNE S Jan. 20, 1959 F.w. CRAWFORD 9,8

EARTH BORING Original Filed Feb. 25 1946 2 Sheets- Sheet 2 5 INVENTOR.

A RWCRAWFORDI ATTORN nnnrn nonmo t Continuation of application SerialNo. 650,105, February 25, 1946, now abandoned. This application October26, 1953, Serial No. 388,175

15. Claims; c1. ass-s s This invention relates to methods and means forearth boring. In a more specific aspect it relates to advancing theearth bore into the ground by one or more explosions in which theexplosive force is directed downwardly, with or without mechanicalrotary drilling operations before or after the explosion or explosions.In another specific aspect it relates to a method and means of loweringan explosive through the rotary drill string and bit so that adownwardly directed explosion may be produced in the well withoutremoving the rotary drilling string.

This application is a continuation of my copending application SerialNo. 650,105 filed February 25, 1946,

for Earth Boring, now abandoned.

In the art of earth boring considerable difiiculty has been experiencedbecause of the existence of very hard formations often encountered inrotary drilling deep oil wells. Often such hard formations are so densethat only a foot ortwo can be rotary drilled in a day or sometimes evena week. Such formations wear out the rotary drilling bit so that it isnecessary to pull outthe rotary drill string to replace the worn outbit. When the well isdeep, considerable time and expense is involved inremovingthe rotary drill string. Therefore, ordinary rotarydrillingmethods become very expensive when such hardformations areencountered, andin some instances rotary'drilling progress hasbecome so.expensive and slow that the well has been abandoned before reaching thedepth desired by geologists.

Thepresent invention is useful in rotary drilling all formations whetherthey are soft or hard. The advantages of the present invention increase,relative to mechanical rotary drilling methods, rapidly as the hardnessof the formations encountered increases. While the present invention isuseful in rotary drilling into a very thick hard formation it isparticularly useful when one or more relatively thin hard formations areencountered, a situation illustrated in Figure l of the drawings.

One object of this invention is to provide means and methods forpenetrating hard formations that are encountered in earth boring.

Another object is to provide means and methods for earth boring.

Another object is to provide means and methods for earth boringemploying one or more downwardly directed explosions each of which mayor may not be preceded or followed by mechanical rotary drilling.

Another object is to provide means and methods for placing the explosivecharges and causing downwardly directed explosions without removing therotary drill string from the well.

A further object of the invention is to provide methods and means forinserting downwardly directed explosions into the usual rotary drillingsystems employed.

Another object is to provide means and methods of running explosives toa point below the bit by means of a wire line tool, or pump-up pump-downtool, usedin atent O 2 place of the usual rotary core barrel orcorebuster of the same type. V

Numerous other objects and advantages will be apparent to those skilledin the art upon reading the action.

Figure 4 is an elevational view, with parts broken away, showing a corebuster which may be substituted for portions of Figure l in practicingcertain embodiments of the present invention.

In Figure 1, an earth bore or well generally designated as 5 is shownextending down through a number of natural earth formations 6, 7,3, 9,10, 11. and 12. An earth formation 13 has been uncovered and it isdesired to penetrate formation .13 and such formations as 14 which liebelow 13.

While the operation of the present invention is not limited by thehardness, or softness, or thickness of the formations, the invention hasparticular advantages in the situation shown in Figure l in whichformations 6, 8, it), 12 and 14 are relatively soft, and formations 7,9, 11 and 13 are particularly hard.

In Figure 1, a rotary drill string generally designated as 15 may be ofany'type old in the art of earth boring. As such it may be a rotarydrill string composed of pipe sections 16 and 17 (Figure 2) connected bycouplings-or tool joints i8. The particular tool joint shown,

joint 18, is a special joint in that it contains an annular groove 19not presentin the other tool joints (not shown). The pipe section 16 maybe provided witha rotary drill collar or coupling 19A to which a rotarydrill bit 193 may be secured.

While rotary drill bit 19B is shown as a roller bit, having rollers 19Cmounted to rotate on bearings 20, it is obvious that other types of bitsemploying fixed blades or rotatable discs may be employed in thepractice of the invention, as rotary drill bit 19B may be any bit founduseful in the prior art as the present invention will operate the samewith any type bit.

Bit 19B however, should contain a large, preferably centrally located,passage 21 so that the explosive charge generally designated as 22may belowered therethrough. Explosive charge 22 isalso generically called atool in the claims along with the other mechanical tools, such as therotary drillingfish tail bit 75, 76, and the rotary core barrel (notshown), which too-ls are adapted to be drilling of a well. The use offirst one tool and then another produces a unitary result of drilling asingle well bore 5 throughvarying formations 6, 7, 8, 9, 10, 11, 12, 13and 14, with the greatest possible speed, and therefore cannot be, saidto be an aggregation. In hard formations 7,9, 11 and. 13 explosive tool22 should be used first, and in soft formations 6, 3, 10, 12 and 14, itis recommended that mechanical .tools be employed, the combination ofthese tools having a unitaryresult of a single straight well: bore 5produced in minimum time. l

Whenexplosive charge 22 is not inside rotary drill string 15, rotarydrill bit 19B may be operated with space 21 empty, or space 21 .may befilled with the usual core barrel or core buster, removable through therotary drill string as will be explained further with relation to Figure4. t r

As shown in Figures 1 and 2, the explosive charge 22 is insertable andremovable through rotary drill string by any of several methods commonin the art of core barrels which are removable throughthe rotary drillstring, the embodiment shown in the drawing being "capable of operationin the same manner as a wire-line rotary core barrel, or a pump-uppump-downtrotary core barrel, as will be explained below underOperation. In the position shown, explosive charge 22 is supported byshoulder 23 of coupling 24 on a corresponding upwardly facing shoulderof rotary drill bit 19B. The lower part of the charge 22 is preferablymade of relatively easily drillable material such as glassor Bakelitebody 25. Numerous suitable materials have been enumerated in'the art ofearth boring, and in the art of wells for use in drillable cementingshoes and collars and for drillable'plugs'for floating easing into thehole, such material being strong but easily rotary drilled through.

While body 25 might be made of a light metal such as magnesium oraluminum, it is preferable to use some glass or plastic compositionbecause such non-metallic I for purposesto be described and an explosivecharge 28 of any suitable explosive is positioned in body 25 preferablysubstantially as shown.

Explosive charge 28 is provided with'a depression 29 preferably in theform of a cone, which depression acts to concentrate most of the forceof the explosives downwardly as will be explained later. Depression 29is preferably lined with arelatively thin layer 30 of any malleable,ductile, and preferably tenacious metal, such as copper, tin, silver, orgold, or alloys having similar properties. Copper or copper alloys arepreferable, as obviously such metals as gold are too expensive to beeconomically employed. This metal layer on explosion of charge 28 seemsto aid the blast of gases coming out of cone 29 to penetrate formation13, but layer 30 is not essential to such operation but is merelypreferable.

Many alternative methods and means for exploding charge 28 can obviouslybe conceived, and the present invention may be'practiced with any suchmeans. For purposes of illustration, however, a much preferred methodand means of exploding charge 28 has been illustrated which has obviousadvantages as pointed out under the operation of the device. This meanscomprises a detonation cap or detonator 31preferably electrically firedby current passing through wires 32 and 33 from dry cell battery 34 whenannular contact 35 connected to wire 32 and central contact 36 connectedto wire 33 completes the circuit by contacting similar contacts 37 and38 connectedto opposite poles of battery 34. While only one cell isshown in battery 34, obviously many cells may be used in series.

Premature contact is prevented by shear pin 39 which will only shear offunder a load of several tons. A helical compression spring 40 may beprovided for holding the contacts apart during assembly, if desired.

Coupling 24 connects body 25 with stand-off body 41. Body 41 has anupper shoulder or inwardly directed flange 42 for shearing shear pin 39and a fluid passage 43 is provided therethrough in order to obviate anyhydraulic lock caused by liquid in space 44.

Battery 34 is retained in the end of piston 45 by means of a threadedcap 46 made of insulating material andcontaining contacts 37 and 38 andthe connecting wires. Contact 38 is spring pressed. As allthese detailsare obvious from the drawings no further discussion 'of' minor parts isgiven.

Piston 45 contains a fluid passage 47, similar "to passage 43 in flange42, and piston 45 is attached to piston rod 48 which continues upwardlyin Figure 2 where his preferably provided with guide'means 49. Guide 49is provided with water passages. In many instances guide 49 isunnecessary and may be eliminated. 'Rod 48 continues upwardly as shownin Figure 2 and has a portion of one side removed to form a plane at 50to provide space for L-shaped latch 51 which is pivoted to rod 48 bywater passage 62 being adapted to be closed by excess down around thecable. cause of less chance of an accident.

means of pivot 52. The lower projecting end 53 of the L-latch 51 may beinserted and removed from the groove 19 as will be described.

Slideably mounted on rod 48 is a sleeve 54. In sleeve 54 is a straightslot 55 cooperating with pin 56 driven into a mating hole in rod 48 toprevent rotation between .rod 48 and sleeve 54. Sleeve 54 may or may notbe provided with water passage 57. Sleeve 54 has a slanting slot 58which acts to guide pin 59. Pin 59 is either integral with the latch oris driven into a hole therein so that as sleeve 54 moves upwardlyrelative to rod 48, the slot 58 will engagev pin 59 and withdraw end 53from grooves 19 by pivoting movement around pivot 52 andvice versa whensleeve 54 moves downward. The sleeve 54 may be provided with afishing-head 60 for engagement with an overshot on a wire line foroperation as a wire line tool. However, an enlarged head 61 is provided,having water passages 62,63 and 64, the center flow valve 65 so that theentire device may be pumped to the surface by the drilling fluid ifdesired as will be explained under the operation.

While a particular type of tool removable through the rotary drillstring has been shown for supporting charge 28, it is obvious that anysuch means old in the art may be substituted in place thereof in thepractice of the invention, except that such devices which are capable ofthe preferred operation of the invention are preferred.

In Figure 3, a much simpler embodiment of the invention is shown,comprising a body 66 preferably made of materials similar to thatdescribed for body 25. Body 66 may contain air spaces 67 and 68.similarrespectively to spaces 26 and 27. Similarly an explosive charge 69,afdetonator70 and wires 71 and 72 are provided which are similar tocorresponding parts 31, 32 and 33. A depression 73 and a metal layer 74'are provided similar to depression 29 and layer 30 of Figure 1 exceptthat the lower edge of 74 is shown lying in a plane which isperpendicular'to the longitudinal axis ofthe apparatus of Figure 3.

Body 66 may be suspended in the well and lowered into the 'well orrotary drill string by means of wires 71 and 72. Wires71 and 72 may bemade into a cable if 'desired. Detonator 70 may havea percussion cap(not shown) extending to the top of body 66, in which case, an ordinaryrope or cable couldreplace wires 71 and '72 and the explosive beactuated. by a go-devil (not shown) which could be a short piece of pipedropped Electric firing is preferred be- Figure 3 is adapted to be usedwith both rotary drill strings and other hollow drill strings, such asshown in Figure 1, in which case it may be lowered through the string orwith cable tools. In the later case the cable tools are preferablyraised or removed from the well to allow :the passage of body 66. Y

In Figure 4, a typical core buster 75 is shown havinga .busters 75, ofFigure 4,has' two .or more splines 79 to engage keyways 78. Obviouslythe number of splines The operation of Figure 4 has already beendescribed with relation to Figures 1 and 2 above.

While this inventionhas been described in connection with certainspecific embodiments, the principle involved is susceptible of numerousother applications that will readily occur to persons skilled in theart. The invention, is therefore, to be limited only as indicated by thescope of the appended claims.

Having thus described the various features of the invention, what Iclaim as new and desire to secure by Letters Patent is: i

1. During the rotary drilling of a borehole with a rotary bit having alongitudinal passage therethrough, the steps comprising lowering intosaid borehole through said bit an explosive charge having a depressionprovided therein to direct the force of the explosion, raising said bitto a point spaced above said charge, positioning said explosive chargeso that said depression will direct the force of said explosive into theearth in the direction of the earth boring, and exploding said chargewhileso positioned, whereby the force of said explosion has asubstantial earth boring effect and other effects are reduced.

2. During the rotary drilling of a borehole with a rotary bit having alongitudinal passage therethrough, the

.steps comprising lowering into said borehole through said hit anexplosive charge having a depression provided therein to direct theforce of the explosion, raising said bit to a point spaced above saidcharge, positioning said explosive charge so that said depression willdirect the force of said explosive into the earth in the direction ofthe earth boring, exploding said charge while so positioned, whereby theforce of said explosion has a substantial earth boring effect and othereffects are reduced, and rotary drilling again with a drilling bit.

, 3. Earth boring apparatus comprising in combination a rotary drillstring having a rotarydrilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid tools, a tool removable through said drill string and positionableon said seat, an explosive charge in said tool having a depressiontherein for directing the force of the explosive downwardly and selfcontained means for firing said charge by downward movement of saiddrilling string comprising an electric circuit actuated by lowering saiddrill string and a detonator in said circuit located in the upperportion of said charge-said tool being constructed to dispose saidexplosive charge a predetermined spaced distance outside said drillingbit and drill string when said tool ispositioned on said seat, saidexplosive charge being connected when so disposed by said tool to saiddrill string and drill bit.

4. Earth boring apparatus comprising in combination a rotary drillstring having a rotary drilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid. tools, a tool removablethrough said drill string and positionableon said seat, an explosive charge in said tool having a depressiontherein for directing the force of the explosive downwardly and selfcontained means for firing said charge by downward movement of saiddrilling string, said tool being constructed to dispose said explosivecharge a predetermined spaced distance outside said drilling-bit anddrill string when said tool is positioned on said seat, said explosivecharge being connected when so disposed by said tool to said drillstring and drill I bit.

5. Earth boring apparatus comprising in combination a rotary drillstring having a rotary drilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid tools, a tool removable through said drill string and positionableon said seat, an explosive charge in said toolhaving a depressiontherein for directing the force of the explosive downwardly and selfcontained means for firing said iii) charge comprising an electriccircuit actuated by lowering said drill string and a detonator in saidcircuit located in said charge, said tool being constructed to disposesaid explosive charge a predetermined spaced distance out side saiddrilling'bita ld drill string when said tool is positioned on said seat,said explosive charge being con nected when so disposed by said tool tosaid drill string and drill bit.

6. Earthboring apparatus comprising in combination a rotary drill stringhaving a rotary drilling bit adapted to receive tools removable throughthe drill string, a seat in said drill string for positioning saidtools, a tool removable through said drill string and positionable onsaid seat, an explosive charge in said tool having a depression thereinfor directing the, force of the explosive downwardly and self containedmeans for firing said charge, said tool being constructed to disposesaid explosive charge apredetermined spaced distance outside saiddrilling bit and drill string when said tool is positioned on said seat,said explosive charge being connected when so disposed by said tool tosaid drill string and drill bit.

7. The method of earth boring comprising rotary drilling with amechanical tool secured to and removable through a rotary drill string,removing the rotary drilling tool and substituting an explosive chargesecured to and positioned a spaced distance in advance of said drillstring without removing the'drill string from the earth bore, explodingthe explosive charge to advance the earth bore, replacing the mechanicaltool in place of the explosive charge and continuing the drilling withthe mechanical tool.

8. The method of claim 7 in which a plurality of explosive charges areplaced andexploded in series before continuing with the mechanicalrotary drilling.

9. Earth boring apparatus comprising in combination a rotarydrill stringhaving a rotary drilling bit adapted to receive an explosive chargeremovable through the drill string, a seat in said drill string forpositioning said explosive charge, an explosive charge removable throughsaid drill string and positionable in said seat in such a manner thatthe lower end thereof extends below said drilling bit, said explosivecharge comprising an elongated member having an explosive charge in itslower end with a depression therein for directing the force of theexplosive downwardly, said elongated member also having a cylinder atits other end, a piston adapted to reciprocate in said cylinder, apiston rod extending from said piston out of said cylinder, a shear pinattached to said piston rod and adapted to press against the upperendofsaid cylinder and to be sheared off when said drill stringis loweredto exert its weight through said piston to cause said piston to beforced into said cylinder, a latch mechanism associated with said pistonrod and adapted to coact with said drill string to hold said piston andpiston rod at a predetermined fixed location therein and a firingmechanism for said charge comprising a detonator in the end of saidcharge opposite said depression, a pair of contact points connected tosaid detonator and located in the lower end of said cylinder, and ashort circuiting means attached to said piston and adapted to connectsaid contact points when said piston is forced into said cylinder aftersaid shear pin is sheared.

10. During the rotary drilling of a borehole with a bit having alongitudinal passage therethrough, the steps comprising lowering intosaid borehole completely through said bit an explosive charge having adepression provided strong.

the hole.

I p 79 is less than the number of keyways 7.8 so that water circulationcontinues.

. .Obviously other core busters and rotary core' barrels old in the artof earth boring may be substituted in place of Figure 4 and I do notclaim Figure 4 to be novel except when employed with my invention, andany other rotary core barrels and core busters may be so employed.

I Operation- The operation of the structure shown in Figures 1 and2is asfollows:

The well driller is rotary drilling with rotary drill string and bit 19Bthrough relatively soft formation 12. During this rotary drilling thecenter opening 21 may be empty or may be filled with a usual rotary"core barrel (not shown) or a core bustensuchas 75 of Figure 4.

Hard formation 13 is then encountered, as in the past hard formations 7,9 and 11 were also encountered. By

many indications at the. surface, such as reduction of cuttings andfailure of the rotary drill string to advance, the driller realizes thathe has encountered a relatively hard formation 13. In the prior art, hewould merely proceed to wear rollers 19C and 76 out on the hardformation, but in the practice of the present invention the drillerraises rotary drill string 15to a position a little higher than thatshown in Figure 1. The driller may continue the circulation of a rotarydrill fluid down through rotary drill string 15 and up the annular spacebetween boreS and rotary drill string 15, or may discontinue circulationas he sees fit. Generally it is preferable to continue circulation.

Obviously, charge 22 is thenlowered into the hole by any of several wellknown methods. It can be lowered on a wire line (not shown) attached to60, or it can be merely dropped into the rotary drill string 15. Drillstring 15 being full of liquid, the dropping is a gentle process and maybe further checked'by a flexible cup '65 which will tend to close hole62 if the progress downward is too rapid. .However, with hole 62completely closed the apparatus may still be pumped down.

However it is lowered, the shoulder 23 takes its seat on the top of bit18 and then sleeve 54 moves downwardly relative to rod 48. Slot 58swings latch 51 by means of pin 59 around pivot 52 so that end 53 isinside annular groove 19. At this time the bottom of body 25 is a shortdistance above the top of formation 13.

The rotary drill string 15 is then lowered until the bottom of body 25contacts formation 13 lifting coupling 24 olf'bit 18 and transmittingcompressive force through shear pin 39, rod 48, pivot 52 and latch 51 tocatch end 53 in groove 19. As the lowering continues no'further circuitbetween ,detonator 31 and battery 34.

Detonator 31 thereupon explodes setting off explosive charge 28. A flamefront or explosive wave passes from detonator 31 downwardly throughcharge 28 progressively increasing in force and due to the presence ofconical depression 29 the force of the explosion is directed along avector down the axis of core 29 into hard formation '13.

While the effect of the explosive charge on the formation depends a loton the character of the formation, in

-many instances the result is that the explosive charge will. blow ahole into'the formation and melt the formation somewhat along the outeredges and the bottom of The extent of the hole depends of course on thethickness and resistance characteristics of formation when rotarydrilling formation 13'before the explosion.

13, but in most cases the situation as to drillability has been improvedthereby. f

While not absolutely essential to the invention, it is preferable tohave an air space 27 spacing explosive28 from the formation 13 in orderto obtain the maximum penetrating-effect of explosive 28, and whilespace 27 could be filled with a liquid such aswater, it is preferred tohave space 27 filled with a gas, it being contemplated to have the gasunder subatmospheric, atmospheric. or superatmospheric pressure. So. faras the explosion is concerned, it is better to have space 27 undersubatmospheric pressure, but in a very deep well, in order toreduce thethickness of 25 it may prove desirable to have the gas in space 27highly compressed in order to aid the walls of 25 in resisting thehydrostatic pressure. On the other hand, it isv simplest and cheapest tohave space 27 at atmospheric pressure and filled with air,,,.al

though an inert gas or a mixture of explosive gases could be employed ifdesired in all threepressure cases mentioned above.

It has been found that the force of explosive 28 is also increased bythe-use of a malleable, ductile and tenacious metal layer 30. The actionduring the explosion is that the layer of metal 30 is turned inside out,

and either in whole, or generally as a number of metal beads, or shot,is driven forcibly into formation 13 increasing the penetration of. theexplosion. 1

Space 26 may be provided to lighten the body 25 and to reduce upwardshock on the rotary drill bit- 191B. However, in many cases space 26 isunnecessary.

The explosion having occurred, the driller may proceed to remove whatremains of 25 by pumping up, or pulling up, head61 in the mannernormalto tools removable through the rotary drill string, such as by awire line (not shown) attached to 60. As sleeve 54 moves up relative torod 48, slot 58 will remove 53 from groove 19, and as 25 had beenshattered there is no pressure opposing the removal. When pin 59 reachesthe bottom of slot 58, rod 48 then is pulled along after head 61 and theremains of the device removed. An annular ridge may be provided aroundthe top of sleeve41 to form a cup to retain the broken ends of shear pin39 if it is necessary to keep them out of the well. Body 25 hasbeenshatteredand the portions thereof remaining in the well being madeof easily drillable material are no ohi stacle for further rotarydrilling. a

The driller then replaces his former rotary core barrel (not shown) orcore buster 75 and proceeds to rotary drill with them. Or he may rotarydrill merely with bit 18 leaving opening 21 empty.

The increased rate of rotary drilling in hard formation ing or reamingof the formation is less hard on the bit,

and is generally productive of more rapid progress than One or moreexplosions may be necessary for each one of formations 7, 9, 11 and 13,and there may or may not be mechanical rotary drilling operation betweenthe succeeding explosions depending upon the drillers judgment andexperience in rotary drilling such formations. Drilling into a verythick,hard fo-rmationmay thus consist of more explosions than mechanicalrotary drilling, but.

fortunately real hard formations have often been found to be thin, beingsometimes only several inches thick.

The operation of Figure 3 is much simpler. The

structure shown in Figure 3 is lowered into thebore 7 hole at anydesired time and exploded while standing on the'bottom, preferably in anupright position, by current from the surface by wires 71 and 72 or by ago-devil' dropped down the supporting cable to set oifa percussion cap(not shown). Regardless of themethod of setting oifthe explosion, theoperation and effect of the explosion is the same as has been describedwith relation to Figures: 1 and 2.

11. Earth boring apparatus comprising in combination a rotary drillstring having a rotary drilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid tools, a tool removable through said drill string and positionableon said seat, an explosive charge in said tool having a depressiontherein for directing the force of the explosive downwardly and selfcontained means for firing said charge by downward movement of saiddrilling string comprising an electric circuit actuated by lowering saiddrill string and a detonator in said circuit located in the upperportion of said charge, said tool and rotary drill bit being soproportioned that when said tool is positioned on said seat said entireexplosive charge has passed through, below and outside said drill bit,and is disposed a predetermined spaced distance below said drill bit,and means to secure said explosive charge to said drill bit whendisposed said spaced distance below said bit.

12. Earth boring apparatus comprising in combination a rotary drillstring having a rotary drilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid tools, a tool removable through said drill string and positionableon said seat, an explosive charge in said tool having a depressiontherein for directing the force of the explosive downwardly and selfcontained means for firing said charge by downward movement of saiddrilling string, said tool and rotary drill bit being so proportionedthat when said tool is positioned on said seat said entire explosivecharge has passed through, below and outside said drill bit, and isdisposed a predetermined spaced distance below said drill bit, and meansto secure said explosive charge to said drill bit when disposed saidspaced distance below said bit.

13. Earth boring apparatus comprising in combination a rotary drillstring having a rotary drilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid tools, a tool removable through said drill string and positionableon said seat, an explosive charge in said tool having a depressiontherein for directing the force of the explosive downwardly andselfcontained means for firing said charge comprising an electric circuitactuated by lowering said drill string and a detonator in said circuitlocated in said charge, said tool and rotary drill bit being soproportioned that whensaid tool is positioned on said seat said entireexplosive charge has passed through, below and outside said, drill bit,and is disposed a predetermined spaced distance below said drill bit,and means to secure said explosive charge to said drill bit whendisposed said spaced distance below said bit.

14. Earth boring apparatus comprising in combination a rotary drillstring having a rotary drilling bit adapted to receive tools removablethrough the drill string, a seat in said drill string for positioningsaid tools, a tool removable through said drill string and positionableon said seat, an explosive charge in said tool having a depressiontherein for directing the force of the explosive downwardly and selfcontained means for firing said charge, said tool and rotary drill bitbeing so proportioned that when said tool is positioned on said seatsaid entire explosive charge has passed through, below and outside saiddrill bit, and is disposed a predetermined spaced distance below saiddrill bit, and means to secure said explosive charge to said drill bitwhen disposed said spaced distance below said bit.

15. During the rotary drilling of a borehole with a rotary bit having alongitudinal passage therethrough, the steps comprising lowering intosaid borehole through said bit a glass enclosed explosive charge havinga depression provided therein to direct the force of the explosion,raising said bit to a point spaced above said charge, positioning saidexplosive charge so that said depression will direct the force of saidexplosive into the earth in the direction of the earth boring, explodingsaid charge while so positioned, whereby the force of said explosion hasa substantial earth boring effect, the glass enclosure is shattered, andother efiects are reduced, and rotary drilling again with a drilling bitto remove the shattered glass and cut into the earth to deepen saidborehole.

References Cited in the file of this patent UNITED STATES, PATENTS OTHERREFERENCES The Shaped Charge, by Volta Torrey, pages to 163 of TheExplosives Engineer, July-August 1945.

